OFFSET
1,2
COMMENTS
Also, indices of the triangular numbers which are sums of three consecutive triangular numbers (see A129803).
LINKS
A. Kozikowska, Topological classes of statically determinate beams with arbitrary number of supports, JOURNAL OF THEORETICAL AND APPLIED MECHANICS 49, 4, pp. 1079-1100, Warsaw 2011; (see Eq. 5.18). - N. J. A. Sloane, Dec 17 2011.
Index entries for linear recurrences with constant coefficients, signature (5,-5,1).
FORMULA
a(n+2)=4*a(n+1)-a(n)+1.
a(n+1)=2*a(n)+0.5+0.5*(12*a(n)^2+12*a(n)-15)^0.5.
G.f.: x*(1-x+x^2)/(1-x)/(1-4*x+x^2). - R. J. Mathar, Oct 24 2007
a(n)-a(n-1)= A005320(n-1). - R. J. Mathar, Mar 14 2016
MATHEMATICA
LinearRecurrence[{5, -5, 1}, {1, 4, 16}, 30] (* Harvey P. Dale, Aug 29 2017 *)
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Richard Choulet, Oct 09 2007
STATUS
approved